Characterizing the integrity of interconnects

ABSTRACT

The present invention provides for a system and method of characterizing the integrity of a barrier structure. The barrier structure is an interconnect comprising a porous dielectric layer sandwiched between at least one barrier layer and at least one conducting layer. The method of characterizing the integrity of such an interconnect includes providing an interconnect, infiltrating the interconnect with a solution comprising electrolytes, applying an external bias to the infiltrated interconnect, and characterizing the integrity of the interconnect after application of the external bias.

BACKGROUND OF THE INVENTION

The present invention relates to the field of electrochemistry, and morespecifically to the characterizing the integrity of diffusion barriers,particularly diffusion barriers in electronic interconnects.

Current electronics typically incorporate multiple layers of complexinterconnect arrays that carry signals to and from its variouscomponents. State of the art electronics are comprised of layers of thinfilm processed metal interconnects (often copper) acting as conductorsas well as dielectric materials that are electrically isolated from theconductors. In order to prevent diffusion and chemical reactions betweenthe conducting material and the dielectric material, a thin layers ofmetal (typically refractory metal or similar material) is typicallyplaced between the conducting and dielectric materials acting adiffusion barrier.

As smaller and higher performance interconnects become increasinglyimportant, the reliability of the diffusion barrier has become critical.Barrier reliability is especially crucial for future technologies as thethickness of these diffusion barriers approach nanoscale dimensions andthe barriers are integrated with dielectric materials (e.g., porouslow-dielectric [low-κ] materials) that will impose more aggressivemechanical and chemical loads. With such very thin diffusion barriers,even small defects are capable of compromising the integrity of thebarrier and instigating various types of functional and physicalfailures of the copper or dielectric material within the interconnectstructure. In addition, relatively thick barriers (e.g., a 25 nm-thickTa diffusion barrier that was sputter-deposited on MSSQ based porouslow-κ dielectric) are capable of failing or, at a minimum, allowing theout-migration and flooding of copper to the dielectric area (e.g., low-κarea) nearby, leaving extensive voids behind.

Such defects and/or failures of diffusion barriers are instigated by atleast two parameters, including ambient and defects in the barrier.Out-migration of Cu, for example, is generally found to be driven by anoxidation potential provided by ambient or a stress gradient. Failure inbarrier integrity is generally triggered by one or more defects in thebarrier. The defect may be present when the barrier was deposited or maydevelop during subsequent processing/fabrication of the interconnect. Toprotect from such failure, strategies for eliminating the driving forcesfor Cu out-diffusion such as ambient infiltration and ways to improvebarrier quality are in order. Unfortunately, these are technicallychallenging, because near perfect barrier coverage must be achievedwhere there is a less thick structure and where physical support for thebarrier layer is lacking. More challenging too is how to characterizeharmful and/or fatal defects in these barriers.

Several methods have been used to characterize the reliability andintegrity of a barrier layer. These include a direct observation of thebarrier microstructure using microscopy, measurement of dielectricbreak-down, biased thermal stressing (BTS), stress migration (SM)testing, and electromigration (EM) testing. Unfortunately, the abovemethods were developed for interconnects with dense dielectric and thickbarrier layers. As such, they are ineffective for detecting harmfuland/or fatal defects in current interconnects, especially thosecomprising sub-microscopic (e.g., nanoscale) diffusion barriers.Further, the above methods are time consuming and not specificallydesigned to examine barrier quality which increases their potential forfalse diagnosis.

The danger of false diagnosis increases when a metallic diffusionbarrier is coupled with a pore-seal layer. The pore-seal layer istypically placed to increase structural and/or chemical stability of thebarrier. A pore seal is typically comprised of a thin layer of densedielectric material deposited prior to deposition of the metallicbarrier layer. Ideally, the pore-seal prevents ingress of processinggases and/or liquids into the dielectric layer (e.g., a porous low-κdielectric) and also provides mechanical support for the barrier and forthe interconnect. Failure of the pore-seal—either completely orpartially—exposes the barrier portion and thin film processed metalportion of the interconnect to the same types of failure as describedabove. Further, with a pore-seal that is defective, the defect and/orfailure is typically local and less extensive and thus, more difficultto detect. Current methods are unable to detect defects and/or failureof a pore seal without extensive and time-consuming examinationgenerally involving several steps and/or equipment.

Therefore, there remains a need to develop a method for evaluatingdiffusion barrier integrity and for detecting defects in a diffusionbarrier and a pore-seal.

SUMMARY OF THE INVENTION

The present invention solves the current problem associated with theinability to characterize the integrity of a diffusion barrier that mayor may not include a pore-seal. By providing a simple, effective andhighly accurate method for detecting defects in diffusion barriers, thepresent invention is capable of being used with thick and thin diffusionbarriers, including barriers integrated with porous low-dielectricconstant (low-κ) materials.

In general, the present invention provides for a system and a method offorming an electrochemical cell, comprising an electrolyte and aninterconnect, under an externally applied bias. The interconnectcomprising at least one diffusion barrier, dielectric material andconducting material. The diffusion barrier may be a refractory metal orother metallic compound. Unlike conventional methods, the resultingbehavior of the present invention provides a means for quantitative andexclusive characterization of barrier integrity and quality.

Generally, and in one form, the present invention provides a system andmethod of characterizing the integrity of a barrier structure, thebarrier structure comprising at least one diffusion barrier integratedwith at least one dielectric layer. The diffusion barrier may, in oneembodiment, surround a dielectric layer, the dielectric layer being aporous low-κ structure or other such porous structure. The diffusionbarrier may also be coupled with a pore-seal. A conducting layer (orpair of electrodes) then surrounds the barrier structure. The integrityof the barrier structure is characterized by voltammetry. When a defectis detected by the present invention, the method may further quantifydefect density, as it is sensitive only to defects in the barrierstructure.

In another form, the present invention provides for a system and methodof characterizing the integrity of any interconnect, the interconnectcomprising a barrier structure and a pair of conducting layers.Typically, the interconnect is a dielectric layer sandwiched between atleast one barrier layer and at least one conducting layer. The formationof an electrochemical cell between the conducting layers (e.g.,refractory metal or other metal) on either side of the barrier structure(diffusion barrier integrated with a dielectric layer) is inducedfollowing introduction of an electrolyte on or about the diffusionbarrier layer via infiltration. The integrity of the diffusion barrier,such as the existence of a defect and the density of defect(s) in thediffusion barrier layer, is then detected by monitoring thereduction-oxidation (redox) potential and current of the conductinglayers under applied bias as characterized by voltammetry. In oneembodiment, the barrier structure comprises a porous dielectric layerthat may or may not be a low-κ dielectric. In yet another embodiment,the barrier structure is coupled with a pore seal. In embodimentswithout a pore-seal, when a diffusion barrier layer is defective, theelectrolyte is connected to the conducting layer through the defect andpeaks associated with a redox reaction appear in a current-voltagevoltammogram. When a pore-seal is absent and the diffusion barrier isdefect-free, the electrolyte is in contact with the diffusion barrier.Absent from a corresponding current-voltage voltammogram are thecharacteristic peaks associated with the redox reaction. Here, the peaksare typically replaced by hysteresis. In embodiments that include apore-seal, a defect-free pore-seal is characterized by electrolytes thatare completely isolated from the conducting layers and a correspondingcurrent-voltage voltammogram will reveal no peaks associated with aredox reaction and no hysteresis. When a pore-seal is present and boththe pore-seal and the diffusion barrier are defective, the conductinglayers are exposed to the electrolytes through the defects in thepore-seal and the barrier, thus, a corresponding current-voltagevoltammogram will reveal the characteristic peaks associated with theredox reaction.

In another form the present invention provides for characterization ofthe integrity of an interconnect as measured with acurrent-capacitance-voltage (ICV) voltammogram. Current is used todetect the presence of an un-reacted component by measuring the peakpotential and comparing the result with the known redox potential of theconducting layer. When a defect is present, a CV voltammogram may revealthe mechanism of the reaction.

As described herein, the integrity of a barrier structure and/orinterconnect may include identifying the presence or absence of adefect, characterizing the interface condition of the interconnectand/or detecting the presence or absence of impurities located in thepores of a barrier structure that is porous. For example, the conditionor profile of a porous diffusion barrier interface may be characterized(e.g., during fabrication or manufacturing) by observing the shape ofthe corresponding current-voltage voltammogram hysteresis. This isbecause the shape of hysteresis is affected by the contact area betweenthe electrolyte and the surface (interface) between the diffusionbarrier and the dielectric layer as well as the roughness of theinterface.

Impurities that are trapped in pores of a barrier structure and/orinterconnect comprising a dielectric layer with an open pore structureare also detected by methods of the present invention. When impuritiesare located in the pores, electrolytes will typically react with theimpurities and produce reaction peaks that may be detected by thepresent invention (i.e., as measured using a current-voltagevoltammogram) when the electrochemical cell is set at a different bias.As such, the presence, type and amount of impurities are characterizedby the present invention.

Other features of the present invention, include its ease of use andcost-effectiveness—it is implemented without any particular investmentbecause it works with a standard test structure and commoninstruments—and its ability to be used for detection of other types ofdefects and/or failures, such as those in a pore seal.

Those skilled in the art will further appreciate the above-notedfeatures and advantages of the invention together with other importantaspects thereof upon reading the detailed description that follows inconjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For more complete understanding of the features and advantages of thepresent invention, reference is now made to the detailed description ofthe invention along with the accompanying figures, wherein:

FIG. 1 depicts a schematic representation of a measurement apparatus inaccordance with one aspect of the present invention;

FIG. 2 depicts an current-voltage (IV) voltammogram taken from a barrierstructure comprising two Cu lines immersed in an electrolyte solutioncomprising 0.5% HCl;

FIG. 3 depicts an IV voltammogram taken from a barrier structurecomprising two tantalum (Ta) lines immersed in 0.5% HCl;

FIG. 4 depicts capacitance change measured during infiltration of 0.1%HCl in an interconnect comprising a standard comb structure with 5μm-wide Cu;

FIG. 5 depicts an I-V voltammogram taken from an interconnect comprisingMSSQ as the porous low-κ layer; and

FIG. 6 depicts a capacitance-voltage (C-V) voltammogram measuredsimultaneously with the I-V voltammogram shown in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Although making and using various embodiments of the present inventionare discussed in detail below, it should be appreciated that the presentinvention provides many inventive concepts that may be embodied in awide variety of contexts. The specific aspects and embodiments discussedherein are merely illustrative of ways to make and use the invention,and do not limit the scope of the invention.

In the description which follows like parts may be marked throughout thespecification and drawing with the same reference numerals,respectively. The drawing figures are not necessarily to scale andcertain features may be shown exaggerated in scale or in somewhatgeneralized or schematic form in the interest of clarity andconciseness.

As used herein, characterizing the integrity of an interconnect requiresthat the interconnect have a barrier structure with a diffusion barrierintegrated with a dielectric layer (typically having an open porestructure), the interconnect comprising at least one diffusion barrier,at least one dielectric layer, and at least one conducting layer. In oneaspect, the conducting layer may form part of the interconnect.

Operation of the present invention is based on the fact that a liquidsolution comprising electrolytes, can infiltrate a barrier structure byinfiltrating the porous portion of the dielectric layer having an openpore structure. The integrity of the barrier structure may then becharacterized through use of voltammetry. Characterization involvesapplication of a potential to a system of the present invention andmeasuring a current response (due to a redox reaction) over a range ofpotentials by a voltage sweep. Species formed by oxidation on the first(forward) scan are reduced on the second (reverse) scan. An estimate ofthe redox potential, rate of electron transfer and stability of thesystem of the present invention are then provided.

Applying the above to an example of the present invention, when abarrier structure is a dielectric layer sandwiched between diffusionbarrier layers and conducting layers (at least one barrier layer andconducting layer on each side), the integrity of the barrier structuremay be measured and quantified after immersion of the barrier structurein a solution containing electrolytes.

In one embodiment, the conducting layer may be Cu. When an electrolyteinfiltrates the Cu interconnect structure, it creates a situationsubstantially the same as an electrochemical cell. The conducting layersact as the electrodes, and are electrically connected through ions inthe electrolyte. When external bias is applied to the two electrodes, anelectrochemical reaction occurs that is dependent on the type ofconducting layer(s) exposed to the electrolyte and the level of theexternal potential. With a barrier that is defect-free, the electrolyteis in contact entirely with the barrier. When a barrier is defective,the electrolyte is also connected to Cu through the defect. In thiscase, the redox reaction of Cu occurs at around +/−0.3V as shown inequation (1) below:Cu^(o)

Cu⁺⁺+2e ⁻  (1)

Since the potential of the more refractory metals is much higher thancopper, the presence of reaction current at +/−0.3V bias indicates thedefective barrier. Furthermore, the current measures the density of thedefects because it is proportional to the area of Cu exposure. Inpractice, the redox potential and current is best characterized by usingcyclic bias (e.g., an IV voltammogram). The area of copper exposurethrough defects in the barrier is also quantified, because the copperredox potential is significantly lower than those of other refractorymetals.

FIG. 1 is a schematic representation of a system of the presentinvention comprising a function generator 10 (e.g., a voltage sweepgenerator) and a pico-ammeter 20 to measure the current while bias istypically cycled at a constant rate (linear or step increase). Apico-ammeter is operably connected to interconnect 60 via 50.Interconnect 60 is on support 70 (e.g., a probe chuck). Support 70 mustbe able to receive an electrolyte solution and may also be one that canbe perfused with an electrolyte solution. Interconnect 60 is at leastone barrier structure sandwiched by at least one conducting layer andcapable of being immersed in a solution of electrolytes.

A capacitance meter 30 is typically included in the system's circuit forcapacitance measurement (FIG. 1). The capacitance meter is operablyconnected to interconnect 60 via 40. Optionally, data analyzer/reader 80is operably connected to the system of FIG. 1 via 85, 90 and/or 95. Thedata analyzer/reader may house additional software for collecting and/orreviewing data about interconnect 60.

Capacitance measurement is important to determine the level ofelectrolyte infiltration. With the present invention, capacitanceincreases as infiltration proceeds because it adds ionic dipoles andshort circuits between conducting layers (or electrodes). Capacitancemeasurement is particularly useful when a pore-seal is placed prior tobarrier deposition; when the pore-seal is intact, capacitance is theonly parameter to indicate electrolyte infiltration.

Useful examples of the present invention are herein provided. In oneembodiment, Example A, a first set of interconnects include a pair of 50μm thick (width) Cu or Ta electrodes patterned on a printed circuitboard (PCB).

In another embodiment, Example B, a second set of interconnects includetwo Cu interconnects patterned in a low dielectric and porous material,such as methylsilsesquioxane (MSSQ, k˜2.2). All samples in Example Bwere processed at International SEMATECH (ISMT) using procedures knownto one of ordinary skill in the art. The samples were fabricated withdifferent diffusion barrier arrangements: 25 nm Ta or 50 nm siliconcarbonitride (SiCN)/0.5 nm Ta. For the SiCN/Ta sample, SiCN wasdeposited by plasma-enhanced chemical vapor deposition (PECVD) and was apore seal, creating a non-porous lining prior to Ta deposition. Aftermetallization, a passivation stack of 100 nm silicon nitride (SiN)/200nm silicon dioxide (SiO₂) was deposited, followed by tantalum nitride(TaN) and aluminum (Al) layers over the bond pad openings. There is nolimit to the pattern that may be used in such a wafer or that may becharacterized by the present invention. For Example B, a standard combtest structure (as provided by ISMT) was selected for the voltammogram.Typically, larger interface area provide for reaction currents that arereadily detectable without interference (e.g., background noise);however, any interface area is suitable to use with the presentinvention.

For the electrolyte solution, any electrolyte solution useful inperforming cyclic voltammetry is suitable. This includes acidic or basicsolutions or those mixed with solvents to assist in infiltration. Withthe present invention, samples were measured in a water-based solutioncontaining at least about 0.1 to 0.5% hydrochloric acid (HCl). InExample A, a voltammogram was conducted by directly immersing thepattern into an electrolyte solution. For Example B, the electrolytesolution was infiltrated through the side of the chip. Typically, thetime for the electrolyte to reach the comb structure was at least about2 minutes to 5 minutes.

FIG. 2 shows results of a cyclic voltammogram conducted on a structureof FIG. 1 with two parallel 50 μm thick Cu electrode on PCB of ExampleA. FIG. 3 shows results of a voltammogram conducted on a structure ofFIG. 1 with two parallel 50 μm thick Ta lines on PCB of Example A. Theelectrolyte solution used for FIG. 2 and FIG. 3 was a 0.5% HCl solutionand the capacitance measurement was done with +/−10 mV signal wave with1 MHz frequency. Typical voltage sweep was +/−0.5 or +/−1V with a rateof 30 mV/s. IV voltammograms from Cu (FIG. 2) and Ta (FIG. 3) aredistinctively different. With a pair of Cu electrodes, peak currentoccurred at a potential at or near +/−0.3, while a peak current wasabsent when a pair of Ta electrodes were used. In FIG. 3, thevoltammogram exhibits a simple hysteresis.

The different voltammogram results for Cu and Ta electrodes areexpected, because when an external bias is applied in anyelectrochemical cell, two types of currents are produced—an ioniccurrent and a reaction current. The voltammogram resulting from Taelectrodes is due to the behavior of refractory Ta electrodes in anionic current. An ionic current is the result of ion drift inelectrolyte under electric potential. With an electrolyte solution ofHCl, hydrogen ions (H₊) drift from anode to cathode while chloride ions(Cl⁻) drifts from cathode to anode. Without a sink and/or source forions in such an electrolyte solution, the ionic current decreases asions accumulate at each electrode because the concentration gradientacts against the external bias. When the bias direction is reversed, theelectric bias and the concentration gradient work together, resulting ininitially high but steadily decreasing ionic current as the ionaccumulation starts to work against the bias. This explains the simplehysteresis for the IV voltammogram with Ta electrodes, because Ta iselectrochemically inert and does not react with the electrolyte in thisbias range. The reaction current exists when electrodes areelectrochemically active and, thus, act as sink and source for ions byprocess of a redox reaction. The redox reaction adds or drains the ionsto or from, respectively, a solution comprising electrolytes, producingan additional current to the background ionic current. Such is the casefor the voltammogram with Cu electrodes, as seen in FIG. 3, where a peakcurrent exists near or at +/−0.3 V. This peak potential is consistentwith the known redox potential of Cu (0.34 V at 25 degrees Centigrade).

As such, methods of the present invention as described above provideclear and concise results applicable to any open electrode structure.For measurement of interconnect structures, methods of the presentinvention are typically conducted after infiltration of an electrolytesolution into or about the interconnect. Because infiltration of anelectrolyte solution into or about the interconnect occurs at arelatively fast rate, there is little reason to delay measurements.Nonetheless, infiltration should be complete. This may be monitored bymeasuring the change in capacitance. For example, the capacitance changeof a comb structure is typically monitored continuously.

FIG. 4 illustrates the capacitance change as measured duringinfiltration of a sample comprising a comb structure. The capacitancemeasurement was done with +/−I 0 mV signal wave with 1 MHz frequency.The capacitance increase is rapid as the electrolyte infiltrates thecomb structure. A steady state value is typically reached within a fewminutes, which is about 3 minutes in the structure measured in FIG. 4.With the present invention, the rapid infiltration rates of theelectrolytes provide for accurate and reliable voltammograms withoutparasitic signals. Importantly, the present invention may be used withany electrolyte solution, sweep condition, and/or diffusion barrier.Data has shown that regardless of the diffusion barrier, the presentinvention is capable of characterizing its integrity.

FIG. 5 shows a voltammogram measurement of Example B, in which thesample is an ISMT comb test structure comprising 0.5 μm Cu interconnectswith 25 nm Ta diffusion barrier in MSSQ porous low-κ dielectric. Thecapacitance measurement was done with +/−10 mV signal wave with 1 MHzfrequency. Here the electrolyte solution was 0.1% HCl. The Cu redox peakwas near +/−0.3 V, therefore, the 25 nm Ta barrier was not defect freebut had defects, likely to be micro-pore and/or pinhole defects, thatexposed a significant fraction of Cu. When the same barrier sample wasevaluated for defects using transmission electron microscope (TEM), nodefects were found (data not shown).

The above failure was verified by testing the sample using BTS andbaking; however, these verification methods were not rapid or efficient,because they took several days to reveal the barrier failure, and werenot as inexpensive as the present invention. In fact, the other methodsare not only more time consuming, they were not conclusive on their ownand required a second analysis or methodology to confirm the mechanismof failure (e.g., TEM analysis after BTS and baking).

There are many valuable features of the present invention. The presentinvention provides conclusive evidence of barrier failure of aninterconnect within minutes to a few hours. Furthermore, because thepeak current is proportional to the area of Cu exposure, the presentinvention also provides a quantitative measure of the defect density asillustrated in FIG. 5. In addition, peak potential is strictly afunction of the chemical redox reaction and remains the same regardlessof test conditions, such as defect density, size of electrodes, andabsence or presence of a low-κ dielectric. Therefore, the presentinvention may be used to detect impurity residues in the pores of anyporous dielectric material, including new refractory compounds (e.g.,TaN and titanium silicon nitride [TiSiN]).

The present invention may be also be used to detect the presence of anun-reacted component by measuring the peak potential and comparing theresult with the known redox potential of the conducting layer or openelectrode structure. As needed, it is useful to incorporate CVvoltammogram measurements to complement the IV measurements of thepresent invention. FIG. 6 shows a CV voltammogram obtainedsimultaneously with the IV voltammogram illustrated in FIG. 5. The CVshows a significant hysteresis in the bias range of the redox potential.This is due to the addition and removal of ionic dipoles. As such, theCV voltammogram measurements support the IV voltammogram findings. CVvoltammograms are, thus, used to reveal the mechanism of reaction (e.g.,whether a peak is a result of the reaction).

In general, the present invention provides for an electrochemicalbehavior of an electrochemical cell formed by electrolyte andinterconnects under cyclic bias. Unlike conventional methods, theresulting voltammogram measurements of the present invention provide ameans for quantitative and exclusive characterization of barrierintegrity and quality.

Use of the present invention is not limited to characterizing theintegrity of a barrier structure. The present invention is also forcharacterizing the integrity of a pore-seal (data not shown). When apore-seal is present, the electrolyte solution is not in electricalconnection with the electrode. Therefore, an IV voltammogram measurementof the present invention will show only the electronic current (leakagecurrent via low-κ layer) when there is an intact pore-seal. On the otherhand, when the pore-seal is not intact, the electrolyte in solution willbecome electrically connected to the underlying metallic layers and anIV voltammogram measurement of the present invention will show ioniccurrent behavior (e.g., if Ta is exposed using an SiCN/Ta sample). Sucha result using a SiCN/Ta sample when Ta was exposed was substantiallysimilar to that shown in FIG. 2. In addition, the extent of thehysteresis was used to measure the density of defects in the pore-seal.

The present invention may be readily modified to suit any particulardiffusion barrier or interconnect and optimized for infiltration of theelectrolyte solution into the sample. Such modifications andoptimizations require no undue experimentation for one of ordinary skillin the art. The present invention works optimally when there issufficient electrolyte solution infiltrating the diffusion barrier. Lessquantitative results arise when the amount of solution is not adequate,because voltammogram measurements will evolve with time. Some ways tokeep a sufficient electrolyte solution infiltrating the diffusionbarrier include minimizing hydrogen gas formation (resulting from theredox reaction of equation [1]) and/or retaining sufficient solution onthe diffusion barrier by placing top-openings near the sample (e.g.,comb pattern) during measurement.

With the present invention, the profile of a barrier-conducting layersurface interface may be characterized when the barrier is a porouslow-κ barrier by observing the shape of the correspondingcurrent-voltage voltammogram hysteresis. The magnitude and shape of thearea within the hysteresis curve may be used to provide a degree ofroughness of the barrier layer surface. This is because the area withinthe hysteresis is a physical representation of the number of ions thathave drifted and have contacted the barrier interface at a given voltagesweep rate. As such, the rougher the barrier surface at this interface,the fatter the hysteresis as compared with one obtained from a barriersurface that is smooth. In addition, the shape of hysteresis (as well asthe magnitude or the area) depends on the profile of the matingelectrode. When the cross section of the interconnects (barrier plusconducting layer or electrode) are of a square profile, the two matingsurfaces of the conducting layer, as they are connected by electrolytesin solution, are a constant distance apart. Here, the change in currentwill be monotonic with increasing and decreasing bias. On the otherhand, when the interconnect cross-section is tapered (e.g., narrower atthe bottom), the mating surfaces are not equidistant. In this case,non-equal distance between two conducting layer (electrode) surfacesleads to ion accumulation that occurs at different rates over thevertical dimension of the conducting surfaces (electrodes). Here, thechange in current is not monotonic with bias. Rather, thecurrent-voltage voltammogram has curvature changes in the hysteresis.

The present invention is also capable of detecting impurities thatinfiltrate a interconnect or diffusion barrier via its dielectric layerhaving an open pore structure. This works in the same manner aspreviously discussed when presenting with two parallel Cu electrode asdescribed for Example A. With the present invention, impurities such asmetallic ions or radicals that have attached to the porous surface arethen dissolved into the solution comprising electrolytes andsubsequently ionized. Upon application of an external bias, the ionsundergo a redox reaction, especially by plating to and dissolving fromthe diffusion barrier surface. Understanding that every ion presentswith a specific redox potential, the specific ion in question isdetermined by applying the appropriate external bias and measuring thepeaks (e.g., at a different potential from Cu, Cu being the conductinglayer) presented with a current-voltage voltammogram. The particular ionas well as the amount trapped in the pore may be measured in thismanner. For example, the redox peak for iron (Fe) is at or near 0.7 Vand the redox peak for titanium (Ti) is at or near 0.2 V which canclearly be distinguished from the redox peak of Cu. As such, when atrapped impurity is suspected, the bias range for the voltammogram isadjusted to the redox potential of the suspected impurity.

While specific alternatives to steps of the invention have beendescribed herein, additional alternatives not specifically disclosed butknown in the art are intended to fall within the scope of the invention.Thus, it is understood that other applications of the present inventionwill be apparent to those skilled in the art upon reading the describedembodiment and after consideration of the appended claims and drawing.

1. A method of characterizing the integrity of an interconnectcomprising the steps of: providing an interconnect portions of whichhave a pore structure; infiltrating the interconnect with a solutioncomprising electrolytes; applying an external bias to the infiltratedinterconnect; and characterizing the integrity of the interconnect afterapplication of the external bias.
 2. The method of claim 1, whereincharacterizing the integrity of the interconnect includes a voltammogramselected from the group consisting of current-voltage,current-capacitance, and current-capacitance-voltage.
 3. The method ofclaim 1 wherein the solution is hydrochloric acid.
 4. The method ofclaim 1, wherein the interconnect comprises a porous dielectric layersandwiched between at least one barrier layer and at least oneconducting layer.
 5. The method of claim 1, wherein the interconnectincludes one of the group consisting of a porous low-dielectric constantmaterial, a pore-seal, and combinations thereof.
 6. The method of claim1, wherein the interconnect is a semiconductor chip.
 7. The method ofclaim 2, wherein the voltammogram provides information about theinterconnect selected from the group consisting of a presence or absenceof a defect, defect density, failure, interface condition, impurities,and combinations thereof.
 8. The method of claim 4, wherein thediffusion barrier is a refractory metal.
 9. The method of claim 4,wherein the conducting layer is copper.
 10. The method of claim 4,wherein the conducting layer forms part of the interconnect.
 11. Asystem for characterizing the integrity of an interconnect comprising:an interconnect immersed in an electrolyte solution, wherein portions ofthe interconnect have a pore structure; a function generator providing apotential and operably connected to the interconnect; a capacitancemeter for measuring capacitance and operably connected to theinterconnect; a picoammeter for measuring current and operably connectedto the interconnect, thereby characterizing the integrity of theinterconnect.
 12. The system of claim 11, wherein characterizing theintegrity of the interconnect includes a voltammogram selected from thegroup consisting of current-voltage, current-capacitance, andcurrent-capacitance-voltage.
 13. The system of claim 11, wherein thesolution is hydrochloric acid.
 14. The method of claim 11, wherein theinterconnect comprises a porous dielectric layer sandwiched between atleast one barrier layer and at least one conducting layer.
 15. Thesystem of claim 11, wherein the interconnect includes one of the groupconsisting of a porous low-dielectric constant material, a pore-seal,and combinations thereof.
 16. The system of claim 11, wherein theinterconnect is a semiconductor chip.
 17. The method of claim 11,further comprising a data reader/analyzer to collect and read data aboutthe integrity of the interconnect.
 18. The system of claim 12, whereinthe voltammogram provides information about the interconnect selectedfrom the group consisting of a presence or absence of a defect, defectdensity, failure, interface condition, impurities, and combinationsthereof.
 19. The method of claim 14, wherein the diffusion barrier is arefractory metal.
 20. The method of claim 14, wherein the conductinglayer is copper.
 21. The method of claim 14, wherein the conductinglayer forms part of the interconnect.